Various types of drive systems for hybrid vehicles are known. For example, Japanese Publication No. 11-082260 shows a hybrid drive system that has a motor/generator disposed between an engine and a transmission. A first clutch is provided to selectively engage and disengage the engine with respect to the motor/generator, and a second clutch is provided to selectively engage and disengage the motor/generator with respect to the transmission.
In a hybrid vehicle having the above-described hybrid drive system, when the first clutch is disengaged and the second clutch is engaged, the electric drive mode is selected, and the vehicle is propelled solely by the motor/generator. On the other hand, when both of the first and second clutches are engaged, the hybrid drive mode is selected, and the vehicle is propelled by both the engine and the motor/generator. When the motor/generator cannot produce sufficient driving during the EV drive mode, the mode changes from the EV drive mode to the HEV drive mode. This mode change is done through an engine start by engaging the first clutch and cranking the engine using an engine-cranking-torque supplied by the motor/generator. Thus, during the mode change from the EV drive mode to the HEV drive mode, the motor/generator is required to supply not only a driving motor torque needed for the EV drive of the vehicle, but also the engine-cranking-torque needed to start the engine.